With the advent of personal computers, there has been an increasing requirement for the transmission of digital data from one locale to another. This requirement will continue to grow as large data bases are accessed by more people electronic checking becomes more wide-spread, electronic purchasing becomes more popular, etc. Similarly, there is a revolution in the facsimile ("fax") transmission field in which fax machines are becoming as common as computers in homes and small offices, and people will transmit papers to each other as regularly as they now make phone calls. All of these applications utilize phone lines for digital data transmission. In single phone line facilities, such as homes or small offices, this creates a problem since the line must be connected to the local data machine if one is expecting to receive or send a digital data message. This makes the phone unavailable for outgoing or incoming voice messages, i.e., conventional telephone calls.
The problem may be solved by installing a separate phone line for each data machine. However, this solution is very costly. Another solution is to require that a human at the sending or receiving end of a phone call make the decision and appropriately connect the local electronics, which is very inconvenient. Therefore, what is needed is an electronic device connected to the local phone line, which determines the nature of each incoming or outgoing phone call (voice call or digital data call) without the need of human assistance and which connects the phone line to the appropriate local equipment after the determination is made. Such a device, if reliable and inexpensive, can pay for itself in a few months because of its convenience and the elimination of the need for multiple phone lines and/or a human operator to route the call.
The above is just one example of the use of a signal analyzing and receiver (or sender) switching device, hereinafter sometimes in abbreviated form referred to as a "voice/data switch", that recognizes the nature of incoming or outgoing calls and that connects the phone line with the appropriate apparatus after determining the nature of each such call without requiring human assistance. The prior art has not been able to satisfactorily fill the need for such a voice/data switch because in the past such devices have not been reliable, have been expensive, have required human assistance, and have not operated on outgoing calls.
Although it may appear simple to distinguish between digital and voice calls, and to connect them to the appropriate equipment, in the past the task has been difficult to handle without human intervention because data machines, such as modems, for example, have widely differing characteristics. Depending on the brand of the modem, it may address the receiving modem with a single, constant pitch tone, a series of digital signals, or silence, to name a few. It becomes particularly difficult to interpret with a machine the meaning of silence; it could be a sending modem awaiting the connection to the data receiver or a human speaker awaiting a spoken response. A machine capable of distinguishing between digital and voice messages only cannot handle such a situation. Moreover, in the past machines of this type were limited to processing one type of call, i.e., either receiving or outgoing calls. The complexity of handling both types of calls and reliably, quickly or transparently analyzing the calls, whether they are digital or voice calls, and doing so without any human intervention, was not solved. The present invention is capable of doing this in an effective, efficient and relatively inexpensive manner.